Are Humans Descended from a Knuckle‐Walking Ancestor?


A central topic in human evolution pertains to the emergence of habitual bipedalism [i.e., upright walking (UW)], a behavioural characteristic that defines the human lineage and is unique among primates. To pinpoint the factors that led to the appearance of UW, one has to reconstruct the locomotor behaviour of the last common ancestor of humans and their closest living relatives, the chimpanzees. Chimpanzees and gorillas adopt a peculiar mode of locomotion when travelling on the ground, knuckle‐walking (KW). This article evaluates the evidence for and against the hypothesis that humans have descended from a KW ancestor. The conflicting nature of this evidence does not allow firm conclusions, but future avenues of research are proposed.

Key Concepts

  • The context for the emergence of habitual bipedalism/upright walking is a key topic in human evolutionary studies.
  • Bipedalism/upright walking is a characteristic that defines the human lineage.
  • Some evidence suggests that the ancestor of the earliest hominins was a knuckle‐walker.
  • However, other evidence appears to contradict this possibility.
  • The role of knuckle‐walking in human evolution will be better understood as more data about the functional anatomy of knuckle‐walking is gathered and as more fossils are described that shed light on the morphology of the last common ancestor of humans and chimpanzees.

Keywords: knuckle‐walking; bipedalism; upright walking; human–chimpanzee last common ancestor; Ardipithecus

Figure 1. Radiographs in medio‐lateral view of the wrist of a common chimpanzee. (a) Extended wrist (support phase). (b) Flexed wrist (swing phase). Reproduced from Richmond and Strait (2000) © Nature Publishing Group.
Figure 2. Evolutionary scenarios for the evolution of bipedalism. (a) Arboreal climbing/clambering ancestor scenario. (b) Knuckle‐walking ancestor scenario. Blue: arboreal climbing; green: knuckle‐walking; red: bipedalism. The revival of the Knuckle‐Walking Hypothesis was spurred by the analysis of molecular data that revealed the existence of a human–chimp clade (to the exclusion of gorillas) as depicted in the phylogenetic trees in (a) and (b).
Figure 3. Illustration of the concept of morphological integration. Each shape and colour represents a character that evolves (arrow) to a new state represented by a new shape and/or colour. When counted separately, it appears that all six traits are independently experiencing evolutionary change. However, if the characters are integrated such that all of the traits evolve in response to a single evolutionary phenomenon, then only a single evolutionary change is needed to explain the evolution of the complex of traits.
Figure 4. Hand and wrist postures during knuckle walking in chimpanzees and gorillas. Reproduced with permission from Kivell and Schmitt (2009) © PNAS.
Figure 5. Palmar view (i.e. from the front) of the distal end of the radius (a forearm bone) that articulates with the bones of the wrist. Arrows indicate the presence of radial dorsal ridge. Reproduced from Richmond and Strait (2000) © Nature Publishing Group.


Begun DR (1992) Miocene fossil hominids and the chimp‐human clade. Science 257: 1929–1933.

Begun DR (1993) Knuckle‐walking ancestors. Science 259: 294.

Begun DR (1994) Relations among the great apes and humans: new interpretations based on the fossil great ape Dryopithecus. Yearbook of Physical Anthropology 37: 11–63.

Begun DR (2004) Knuckle‐walking and the origin of human bipedalism. In: Meldrum DJ and Hilton CE, (eds). From Biped to Strider: The emergence of modern human walking, running, and resource transport, pp. 9–33. New York: Kluwer.

Corruccini RS (1978) Comparative osteometrics of the hominoid wrist joint, with special reference to knuckle‐walking. Journal of Human Evolution 7: 307–321.

Corruccini RS and McHenry HM (2001) Knuckle‐walking hominid ancestors. Journal of Human Evolution 40: 507–511.

Dainton M and Macho GA (1999) Did knuckle walking evolve twice? Journal of Human Evolution 36: 171–194.

Fleagle JG, Stern JT, et al. (1981) Climbing: a biomechanical link with brachiation and bipedalism. Symposium of the Zoological Society of London 48: 359–373.

Hunt KD (1996) The postural feeding hypothesis: an ecological model for the evolution of bipedalism. South African Journal of Science 92: 77–90.

Ishida H, Kumakura H and Kondo S (1985) Primate bipedalism and quadrupedalism: comparative electromyography. In: Kondo S, (ed). Primate morphophysiology, locomotor analyses and human bipedalism, pp. 59–79. Tokyo: University of Tokyo Press.

Jenkins FAJ and Fleagle JG (1975) Knuckle‐walking and the functional anatomy of the wrists in living apes. In: Tuttle RH, (ed). Primate Functional Morphology and Evolution, pp. 213–231. The Hague: Mouton.

Kimbel WH, Suwa G, Asfaw B, et al. (2014) Ardipithecus ramidus and the evolution of the human cranial base. Proceedings of the National Academy of Sciences of the United States of America 111: 948–953.

Kivell TL and Schmitt D (2009) Independent evolution of knuckle‐walking in African apes shows that humans did not evolve from a knuckle‐walking ancestor. Proceedings of the National Academy of Sciences 106: 14241–14246.

Lovejoy CO, Suwa G, Spurlock L, et al. (2009a) The pelvis and femur of Ardipithecus ramidus: the emergence of upright walking. Science 326: 71e1–71e6.

Lovejoy CO, Simpson SW, White TD, et al. (2009b) Careful climbing in the Miocene: the forelimbs of Ardipithecus ramidus and humans are primitive. Science 326: 70e1–70e8.

Olson EC and Miller RL (1958) Morphological Integration. Chicago, IL: University of Chicago Press.

Prost JH (1980) Origin of bipedalism. American Journal of Physical Anthropology 52: 175–189.

Richmond BG and Strait DS (2000) Evidence that humans evolved from a knuckle‐walking ancestor. Nature 202: 382–385.

Richmond BG and Strait DS (2001) Did our human ancestors knucklewalk? Nature 410: 326.

Richmond BG, Begun DR and Strait DS (2001) Origins of human bipedalism: the knuckle‐walking hypothesis revisited. Yearbook of Physical Anthropology 44: 70–105.

Richmond BG (2006) Functional morphology of the midcarpal joint in knuckle‐walkers and terrestrial quadrupeds. In: Ischida H, Tuttle R, Pickford M, et al., (eds). Human Origins and Environmental Backgrounds, pp. 105–122. Chicago, IL: Springer.

Rodman PS and McHenry HM (1980) Bioenergetics and the origin of hominid bipedalism. American Journal of Physical Anthropology 52: 103–106.

Senut B (1988) Climbing as a crucial preadaptation for human bipedalism. International Journal of Skeletal Research 14: 35–44.

Shea BT and Inouye SE (1993) Knuckle‐walking ancestors. Science 259: 293–294.

Stern JT, Jr (1975) Before bipedality. Yearbook of Physical Anthropology 19: 59–68.

Stern JT, Jr and Susman RL (1981) Electromyography of the gluteal muscles in Hylobates, Pongo, and Pan: implications for the evolution of hominid bipedality. American Journal of Physical Anthropology 55: 153–166.

Suwa G, Asfaw B, Kono RT, et al. (2009) The Ardipithecus ramidus skull and its implications for hominid origins. Science 326: 68e1–68e7.

Taylor CR and Rowntree VJ (1973) Running on two or on four legs: Which consumes more energy? Science 179: 186–87.

Thorpe SKS, Holder RL and Cromption RH (2007) Origin of human bipedalism as an adaptation for locomotion of flexible branches. Science 316: 1328–1331.

Tuttle RH (1967) Knuckle‐walking and the evolution of hominoid hands. American Journal of Physical Anthropology 26: 171–206.

Tuttle RH (1969) Knuckle‐walking and the problem of human origins. Science 166: 953–961.

Tuttle RH (1974) Darwin's apes, dental apes, and the descent of man: normal science in evolutionary anthropology. Current Anthropology 15: 389–398.

Washburn SL (1967) Behavior and the origin of man. Proceedings of the Royal Anthropological Institute of Great Britain and Ireland 3: 21–27.

White TD, Asfaw B, Beyene Y, et al. (2009) Ardipithecus ramidus and the paleobiology of early hominids. Science 326: 64–86.

Williams SA (2010) Morphological integration and the evolution of knuckle‐walking. Journal of Human Evolution 58: 432–440.

Wood B and Harrison T (2011) The evolutionary context of the first hominins. Nature 470: 347–352.

Further Reading

Harrison T (2010) Apes among the tangled branches of human origins. Science 237: 532–534.

Wang W, Abboud RJ, Günther MM and Crompton RH (2014) Analysis of joint force and torque for the human and non‐human ape foot during bipedal walking with implications for the evolution of the foot. Journal of Anatomy 225 (2): 152–166.

Wood, BA (2001) Human Evolution: Early Radiations. eLS. John Wiley & Sons Ltd, Chichester. 10.1038/npg.els.0001648

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Makedonska, Jana A, and Strait, David S(May 2015) Are Humans Descended from a Knuckle‐Walking Ancestor?. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0026161]